RAC1 and breast cancer: Interestingly, Rac1 P29S (which has also been found as a somatic mutation in a breast cancer cell line) transformed MCF10A cells more efficiently than fibroblasts, whereas the opposite was true for the Rac1 N92I mutation (known as a somatic mutation in a fibrosarcoma cell line),96 suggesting that there are further subtleties to the effects of these different activating mutations still to be uncovered.